1. Field of the invention
The present invention relates to a head-up display device, of holographic type and equipped with a simplified relay optics.
2. Description of the prior art
The present invention relates more particularly to head-up displays whose known architecture comprises essentially a generator for a luminous image to display, an holographic optical element, and a relay optics that produces an intermediate image of the luminous image in the focal plane of the holographic optical element, which element plays the role of a combining optics so that the observer sees both the collimated luminous image reflected by this element and the outside world through this element. In addition, a folding optics provided with a reflecting side is disposed between the relay optics and the holographic optical element. The latter is advantageously implemented on a spherical substrate including an hologram and used in an out-of-axis position.
A sight structure of this type is described in particular in the publication "Proceedings of the IEEE, 1982 National Aerospace and Electronics Conference" (NAECON), 1982, volume 2, pages 752 to 759, in a paper of Jerold H. GARD with the title "Holographic HUDs De-mystified"; in this publication, one can in particular refer to FIG. 15 and the related text.
This kind of device exhibits numerous aberrations due to the use of an out-of-axis holographic optics. To correct these defects, a relay optics is used that produces an intermediate image but this optics is generally complex, difficult to define and its correcting ability is limited.
The general trend and the purpose of the present invention are to simplify as much as possible this relay optics and to increase its performance.
A known solution described in the American patent U.S. Pat. No. 4,218,111 and in the corresponding European patent EP-B1-0 007 039 shows a relay optics reduced to nine elements comprising a plane element that is the screen of the cathode-ray tube itself, seven lenses some of which are tilted or out of axis, and an optical filter; in addition, a thenth element playing a correcting role is constituted by a folding prism forming a Mangin mirror.
A further object of the invention is to remedy the complexity of the relay optics by proposing a simplified scheme reduced to six optical lenses. Other features and advantages results in particular from the holographic optical element and the relay optics being computed taking into account the average curvature of the windshield, which allows to manufacture a standard relay optics that exhibits interchangeability aspects on aircraft of one and the same type; the precise matching of this system is performed on an intermediate optical element without optical power constituted by a closing glass plate disposed in the optical path from the folding optical element to the combining holographic element.